string imap_last_error ( void ) - Gets the full text of the last IMAP error message that occurred on the current page. The error stack is untouched; calling imap_last_error() subsequently, with no intervening errors, will return the same error.

bool imap_ping ( resource $imap_stream ) - imap_ping() pings the stream to see if it's still active. It may discover new mail; this is the preferred method for a periodic new mail check as well as a keep alive for servers which have inactivity timeout.

int imap_uid ( resource $imap_stream , int $msg_number ) - This function returns the UID for the given message sequence number. An UID is a unique identifier that will not change over time while a message sequence number may change whenever the content of the mailbox changes.